Pre-heat oven to 400 degrees. Mix 1/2 cup sugar and the cornstarch in 2-quart saucepan. Add the blueberries and lemon juice. Cook over medium heat stirring constantly, until mixture thickens and boils. Keep to boil as you stir constantly for 1 minute and then pour the mixture into ungreased 2-quart casserole. Place in the hot oven to keep blueberry mixture hot. Next, cut the shortening into flour, add 1 tablespoon sugar, the baking powder and salt until mixture resembles fine crumbs. Stir in the milk until dough forms. Drop the dough by 6 spoonfuls onto hot blueberry mixture. Bake 25 to 30 minutes or until topping is golden brown. Serve warm topping with your favorite whipped cream or whipped topping!